Reducing location-dependent interference in distributed antenna systems operating in multiple-input, multiple-output (mimo) configuration, and related components, systems, and methods

ABSTRACT

Components, systems, and methods for reducing location-based interference in distributed antenna systems operating in multiple-input, multiple-output (MIMO) configuration are disclosed. Interference is defined as issues with received MIMO communications signals that can cause a MIMO algorithm to not be able to solve a channel matrix for MIMO communications signals received by MIMO receivers in client devices. These issues may be caused by lack of spatial (i.e., phase) separation in the received MIMO communications signals. Thus, to provide phase separation of received MIMO communication signals, multiple MIMO transmitters are each configured to employ multiple transmitter antennas, which are each configured to transmit in different polarization states. In certain embodiments, one of the MIMO communications signals is phase shifted in one of the polarization states to provide phase separation between received MIMO communication signals. In other embodiments, multiple transmitter antennas in a MIMO transmitter can be offset to provide phase separation.

PRIORITY APPLICATION

This application is a continuation of U.S. patent application Ser. No. 14/487,232, filed Sep. 16, 2014, which is a continuation of International Application No. PCT/US13/034328, filed on Mar. 28, 2013, which claims priority under 35 U.S.C. §119 to U.S. Provisional Patent Application No. 61/618,396, filed on Mar. 30, 2012, the contents of which are relied upon and incorporated herein by reference in their entireties.

RELATED APPLICATION

This application is related to U.S. Provisional Patent App. No. 61/541,566, filed on Sep. 30, 2011, which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Disclosure

The technology of the disclosure relates to distribution of data (e.g., digital data services and radio-frequency communications services) in a distributed antenna system.

2. Technical Background

Wireless customers are demanding digital data services, such as streaming video signals. Concurrently, some wireless customers use their wireless devices in areas that are poorly served by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of distributed antenna systems. Distributed antenna systems can be particularly useful to be deployed inside buildings or other indoor environments where client devices may not otherwise be able to effectively receive radio-frequency (RF) signals from a source. Distributed antenna systems include remote units (also referred to as “remote antenna units”) configured to receive and wirelessly transmit wireless communications signals to client devices in antenna range of the remote units. Such distributed antenna systems may use Wireless Fidelity (WiFi) or wireless local area networks (WLANs), as examples, to provide digital data services.

Distributed antenna systems may employ optical fiber to support distribution of high bandwidth data (e.g., video data) with low loss. Even so, WiFi and WLAN-based technology may not be able to provide sufficient bandwidth for expected demand, especially as high definition (HD) video becomes more prevalent. WiFi was initially limited in data rate transfer to 12.24 Mb/s and is provided at data transfer rates of up to 54 Mb/s using WLAN frequencies of 2.4 GHz and 5.8 GHz. While interesting for many applications, WiFi bandwidth may be too small to support real time downloading of uncompressed high definition (HD) television signals to wireless client devices.

Multiple-input, multiple-output (MIMO) technology can be employed in distributed antenna systems to increase the bandwidth up to twice the nominal bandwidth, as a non-limiting example. MIMO is the use of multiple antennas at both a transmitter and receiver to increase data throughput and link range without additional bandwidth or increased transmit power. However, even doubling bandwidth alone may not be enough to support high bandwidth data to wireless client devices, such as the example of real time downloading of uncompressed high definition (HD) television signals.

The frequency of wireless communications signals could also be increased in a MIMO distributed antenna system to provide larger channel bandwidth as a non-limiting example. For example, an extremely high frequency (EHF) in the range of approximately 30 GHz to approximately 300 GHz could be employed. For example, the sixty GHz (60 GHz) spectrum is an EHF that is an unlicensed spectrum by the Federal Communications Commission (FCC). EHFs could be employed to provide for larger channel bandwidths. However, higher frequency wireless signals are more easily attenuated and/or blocked from traveling through walls, building structures, or other obstacles where distributed antenna systems are commonly installed. Higher frequency wireless signals also provide narrow radiation patterns. Thus, remote units in distributed antenna systems may be arranged for line-of-sight (LOS) communications to allow for higher frequencies for higher bandwidth. However, if remote units are provided in a LOS configuration, and the remote units are also configured to support MIMO, multiple data streams in the same frequency channel will be received by multiple receiver antennas in the remote units. This can lead to multiple data streams received in the same frequency channel leading to performance degradation and limited wireless coverage where the MIMO algorithm can fail to solve the channel matrix.

SUMMARY OF THE DETAILED DESCRIPTION

Components, systems, and methods for reducing location-based interference in distributed antenna systems operating in multiple-input, multiple-output (MIMO) configuration are disclosed. The distributed antenna systems include remote units employing MIMO transmitters configured to transmit multiple data streams in MIMO configuration to MIMO receivers in wireless client devices. Interference is defined as issues with received MIMO communications signals that can cause a MIMO algorithm to not be able to solve a channel matrix for MIMO communications signals received by MIMO receivers in client devices. These issues can occur due to lack of spatial (i.e., phase) separation in the received MIMO communications signals, especially with closely located MIMO transmitters configured for line-of-sight (LOS) communications. Thus, to provide phase separation of MIMO communication signals received by MIMO receivers in client devices, multiple MIMO transmitters in a remote unit are each configured to employ multiple transmitter antennas, which are each configured to transmit in different polarization states. In certain embodiments, one of the MIMO communications signals is phase shifted in one of the polarization states to provide phase separation between MIMO communication signals received by the MIMO receivers. In other embodiments, multiple transmitter antennas in a MIMO transmitter can be offset to provide phase separation.

The components, systems, and methods for location-based interference in a distributed antenna systems operating in MIMO configuration may significantly improve high-data rate wireless coverage without significant dependence on transmitter and/or receive placement. This may allow for LOS communications to be more easily achieved, especially for higher frequency communications where LOS communications may be employed to reduce the effect of obstacles. High antenna isolation is not required in the MIMO receivers. The increased coverage area can also allow for higher efficiency at higher frequencies typically inefficient for radio frequency (RF) amplifiers.

In this regard, in one embodiment, a MIMO remote unit configured to wirelessly distribute MIMO communications signals to wireless client devices in a distributed antenna system is provided. The MIMO remote unit comprises a first MIMO transmitter comprising a first MIMO transmitter antenna configured to transmit MIMO communications signals in a first polarization and a second MIMO transmitter antenna configured to transmit MIMO communications signals in a second polarization different from the first polarization. The MIMO remote unit also comprises a second MIMO transmitter comprising a third MIMO transmitter antenna configured to transmit MIMO communications signals in the first polarization and a fourth MIMO transmitter antenna configured to transmit MIMO communications signals in the second polarization. The first MIMO transmitter is configured to receive a first downlink MIMO communications signal in a first phase over a first downlink communications medium, and transmit the first downlink MIMO communications signal wirelessly as a first electrical downlink MIMO communications signal over the first MIMO transmitter antenna in the first polarization. The first MIMO transmitter is also configured to receive a second downlink MIMO communications signal in the first phase over a second downlink communications medium, and transmit the second downlink MIMO communications signal wirelessly as a second electrical downlink MIMO communications signal over the second MIMO transmitter antenna in the second polarization. The second MIMO transmitter is configured to receive a third downlink MIMO communications signal in the first phase over a third downlink communications medium, and transmit the third downlink MIMO communications signal wirelessly as a third electrical downlink MIMO communications signal over the third MIMO transmitter antenna in the first polarization. The second MIMO transmitter is also configured to receive a fourth downlink MIMO communications signal over a fourth downlink communications medium, and transmit the fourth downlink MIMO communications signal in a second phase shifted from the first phase, wirelessly as a fourth electrical downlink MIMO communications signal over the fourth MIMO transmitter antenna in the second polarization.

In another embodiment, a method of transmitting MIMO communications signals to wireless client devices in a distributed antenna system is provided. The method includes receiving a first downlink MIMO communications signal in a first phase over a first downlink communications medium. The method also includes transmitting the first downlink MIMO communications signal wirelessly as a first electrical downlink MIMO communications signal over a first MIMO transmitter antenna in a first polarization. The method also includes receiving a second downlink MIMO communications signal in the first phase over a second downlink communications medium. The method also includes transmitting the second downlink MIMO communications signal wirelessly as a second electrical downlink MIMO communications signal over a second MIMO transmitter antenna in a second polarization. The method also includes receiving a third downlink MIMO communications signal in the first phase over a third downlink communications medium. The method also includes transmitting the third downlink MIMO communications signal wirelessly as a third electrical downlink MIMO communications signal over the third MIMO transmitter antenna in the first polarization. The method also includes receiving a fourth downlink MIMO communications signal over a fourth downlink communications medium. The method also includes transmitting the fourth downlink MIMO communications signal in a second phase shifted from the first phase, wirelessly as a fourth electrical downlink MIMO communications signal over the fourth MIMO transmitter antenna in the second polarization.

In another embodiment, a distributed antenna system for distributing MIMO communications signals to wireless client devices is provided. The distributed antenna system comprises a central unit. The central unit comprises a central unit transmitter configured to receive a downlink communications signal. The central unit transmitter is also configured to transmit the received downlink communications signal as a first MIMO downlink communications signal over a first downlink communications medium, a second MIMO downlink communications signal over a second downlink communications medium, a third MIMO downlink communications signal over a third downlink communications medium, and a fourth MIMO downlink communications signal over a fourth downlink communications medium.

This distributed antenna system also comprises a remote unit. The remote unit comprises a first MIMO transmitter comprising a first MIMO transmitter antenna configured to transmit MIMO communications signals in a first polarization and a second MIMO transmitter antenna configured to transmit MIMO communications signals in a second polarization different from the first polarization. The remote unit also comprises a second MIMO transmitter comprising a third MIMO transmitter antenna configured to transmit MIMO communications signals in the first polarization and a fourth MIMO transmitter antenna configured to transmit MIMO communications signals in the second polarization. The first MIMO transmitter is configured to receive a first downlink MIMO communications signal in a first phase over a first downlink communications medium, and transmit the first downlink MIMO communications signal wirelessly as a first electrical downlink MIMO communications signal over the first MIMO transmitter antenna in the first polarization. The first MIMO transmitter is also configured to receive a second downlink MIMO communications signal in the first phase over a second downlink communications medium, and transmit the second downlink MIMO communications signal wirelessly as a second electrical downlink MIMO communications signal over the second MIMO transmitter antenna in the second polarization. The second MIMO transmitter is configured to receive a third downlink MIMO communications signal in the first phase over a third downlink communications medium, and transmit the third downlink MIMO communications signal wirelessly as a third electrical downlink MIMO communications signal over the third MIMO transmitter antenna in the first polarization. The second MIMO transmitter is also configured to receive a fourth downlink MIMO communications signal over a fourth downlink communications medium, and transmit the fourth downlink MIMO communications signal in a second phase shifted from the first phase, wirelessly as a fourth electrical downlink MIMO communications signal over the fourth MIMO transmitter antenna in the second polarization. The remote unit also comprises at least one phase shifter configured to phase shift the fourth downlink MIMO communications signal to the second phase.

The distributed antenna systems disclosed herein can be configured to support one or more radio-frequency (RF)-based services and/or distribution of one or more digital data services. The remote units in the distributed antenna systems may be configured to transmit and receive wireless communication signal at one or more frequencies, including but not limited to extremely high frequencies (EHF) (i.e., approximately 30 GHz—approximately 300 GHz). The distributed antenna systems may include, without limitation, wireless local area networks (WLANs). Further, as a non-limiting example, the distributed antenna systems may be an optical fiber-based distributed antenna system, but such is not required. An optical fiber-based distributed antenna system may employ Radio-over-Fiber (RoF) communications. The embodiments disclosed herein are also applicable to other remote antenna clusters and distributed antenna systems, including those that include other forms of communications media for distribution of communications signals, including electrical conductors and wireless transmission. For example, the distributed antenna systems may include electrical and/or wireless communications mediums between a central unit and remote units in addition or in lieu of optical fiber communications medium. The embodiments disclosed herein may also be applicable to remote antenna clusters and distributed antenna systems and may also include more than one communications media for distribution of communications signals (e.g., digital data services, RF communications services). The communications signals in the distributed antenna system may or may not be frequency shifted.

It is to be understood that both the foregoing general description and the following detailed description present embodiments, and are intended to provide an overview or framework for understanding the nature and character of the disclosure. The drawings illustrate various embodiments, and together with the description serve to explain the principles and operation of the concepts disclosed.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic of an exemplary distributed antenna system;

FIG. 2 is a schematic diagram of an exemplary multiple-in, multiple-out (MIMO) optical fiber-based distributed antenna system;

FIG. 3A is a top view diagram of a room having an exemplary MIMO antenna system comprising two (2) MIMO transmitter antennas in line-of-sight (LOS) with two (2) MIMO receiver antennas to illustrate interference in MIMO communication signals received in the same frequency channel by the MIMO receiver antennas that can cause a MIMO algorithm to fail to solve the channel matrix;

FIG. 3B is a graph illustrating exemplary measured performance degradation for a given placement distance between the MIMO transmitter antennas in the MIMO antenna system in FIG. 3A;

FIG. 3C is a graph illustrating an exemplary effective antenna coverage area in proximity to the MIMO transmitter antennas in FIG. 3A;

FIG. 4A is a schematic diagram of an exemplary MIMO optical fiber-based distributed antenna system employing a central unit employing a MIMO transmitter configured to electrically phase shift at least one transmitted MIMO electrical downlink communications signal received and transmitted by a remote unit employing multiple MIMO transmitters each configured with multiple MIMO transmitter antennas configured to transmit in different polarization states;

FIG. 4B is a schematic diagram of an exemplary MIMO optical fiber-based distributed antenna system employing an optical phase shifter in an optical downlink communications medium configured to optically phase shift at least one transmitted MIMO electrical downlink communications signal received and transmitted by a remote unit employing multiple MIMO transmitters each configured with multiple MIMO transmitter antennas configured to transmit in different polarization states;

FIG. 4C is a schematic diagram of an exemplary MIMO optical fiber-based distributed antenna system employing remote units employing multiple MIMO transmitters each employing multiple MIMO transmitter antennas configured to transmit in different polarization states, wherein one of the MIMO electrical downlink communications signals transmitted by one of the MIMO transmitters in a polarization state is electrically phase shifted;

FIG. 5A is a graph illustrating exemplary measured performance degradation for a given placement distance between MIMO transmitter antennas in a MIMO transmitter in a remote unit in the distributed antenna systems in FIGS. 4A-4C, when employing and not employing phase shifting of at least one transmitted downlink communications signals;

FIG. 5B is a graph illustrating an exemplary effective antenna coverage area in proximity to the MIMO transmitter antennas of a remote unit in the distributed antenna systems in FIGS. 4A-4C;

FIG. 5C is a graph illustrating an exemplary effective antenna coverage versus placement distance between MIMO transmitter antennas in a MIMO transmitter in a remote unit in the distributed antenna systems in FIGS. 4A-4C, for a given first placement distance between MIMO receiver antennas, when employing and not employing phase shifting of at least one transmitted downlink communications signals;

FIG. 5D is a graph illustrating an exemplary effective antenna coverage versus placement distance between MIMO transmitter antennas in a MIMO transmitter in a remote unit in the distributed antenna systems in FIGS. 4A-4C, for a given second placement distance between MIMO receiver antennas, when employing and not employing phase shifting of at least one transmitted downlink communications signal;

FIG. 6 is a schematic diagram of an exemplary remote unit in a MIMO distributed antenna system, wherein the remote unit employs multiple MIMO transmitters, and wherein at least one of the MIMO transmitters provides an offset between its multiple MIMO transmitters antennas configured to transmit in different polarization states;

FIG. 7A is a graph illustrating an exemplary effective antenna coverage versus placement distance between MIMO transmitter antennas in a MIMO transmitter of the remote unit in FIG. 6, for a given first placement distance between MIMO receiver antennas, when employing and not employing placement offset between the MIMO transmitter antennas;

FIG. 7B is a graph illustrating an exemplary effective antenna coverage versus placement distance between MIMO transmitter antennas in a MIMO transmitter of the remote unit in FIG. 6, for a given second placement distance between MIMO receiver antennas, when employing and not employing placement offset between MIMO transmitter antennas;

FIG. 7C is a graph illustrating an exemplary effective antenna coverage for a given placement distance between MIMO transmitter antennas, in a MIMO transmitter of the remote unit in FIG. 6, for a given placement distance between MIMO receiver antennas, when employing and not employing placement offset between MIMO transmitter antennas; and

FIG. 8 is a schematic diagram of a generalized representation of an exemplary controller that can be included in any central unit, remote units, wireless client devices, and/or any other components of distributed antenna systems to reduce or eliminate issues with a MIMO algorithm solving the channel matrix for transmitted MIMO electrical downlink communications signals.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples of which are illustrated in the accompanying drawings, in which some, but not all embodiments are shown. Indeed, the concepts may be embodied in many different forms and should not be construed as limiting herein; rather these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Whenever possible, like reference numbers will be used to refer to like components or parts.

Components, systems, and methods for reducing location-based interference in distributed antenna systems operating in multiple-input, multiple-output (MIMO) configuration are disclosed. The distributed antenna systems include remote units employing MIMO transmitters configured to transmit multiple data streams in MIMO configuration to MIMO receivers in wireless client devices. Interference is defined as issues with received MIMO communications signals that can cause a MIMO algorithm to not be able to solve a channel matrix for MIMO communications signals received by MIMO receivers in client devices. These issues can occur due to lack of spatial (i.e., phase) separation in the received MIMO communications signals, especially with closely located MIMO transmitters configured for line-of-sight (LOS) communications. Thus, to provide phase separation of MIMO communication signals received by MIMO receivers in client devices, multiple MIMO transmitters in a remote unit are each configured to employ multiple transmitter antennas, that are each configured to transmit in different polarization states. In certain embodiments, one of the MIMO communications signals is phase shifted in one of the polarization states to provide phase separation between MIMO communication signals received by the MIMO receivers. In other embodiments, multiple transmitter antennas in a MIMO transmitter can be offset to provide phase separation.

Before discussing examples of components, systems, and methods for reducing location-based interference in distributed antenna systems operating in MIMO configuration starting at FIG. 4A, an exemplary distributed antenna system is described in regard to FIGS. 1-3C. In this regard, FIG. 1 is a schematic diagram of a conventional distributed antenna system 10. The distributed antenna system 10 is an optical fiber-based distributed antenna system. The distributed antenna system 10 is configured to create one or more antenna coverage areas for establishing communications with wireless client devices located in the radio frequency (RF) range of the antenna coverage areas. In an exemplary embodiment, the distributed antenna system 10 may provide RF communication services (e.g., cellular services). As illustrated, the distributed antenna system 10 includes a central unit 12, one or more remote units 14, and an optical fiber 16 that optically couples the central unit 12 to the remote unit 14. The central unit 12 may also be referred to as a head-end unit. The remote unit 14 is a type of remote communications unit, and may also be referred to as a “remote antenna unit.” In general, a remote communications unit can support wireless communications or wired communications, or both. The central unit 12 is configured to receive communications over downlink electrical RF signals 18D from a source or sources, such as a network or carrier as examples, and provide such communications to the remote unit 14. The central unit 12 is also configured to return communications received from the remote unit 14, via uplink electrical RF signals 18U, back to the source or sources. In this regard, in this embodiment, the optical fiber 16 includes at least one downlink optical fiber 16D to carry signals communicated from the central unit 12 to the remote unit 14 and at least one uplink optical fiber 16U to carry signals communicated from the remote unit 14 back to the central unit 12.

One downlink optical fiber 16D and one uplink optical fiber 16U could be provided to support multiple full-duplex channels each using wave-division multiplexing (WDM), as discussed in U.S. patent application Ser. No. 12/892,424, entitled “Providing Digital Data Services in Optical Fiber-based Distributed Radio Frequency (RF) Communications Systems, And Related Components and Methods,” incorporated herein by reference in its entirety. Other options for WDM and frequency-division multiplexing (FDM) are also disclosed in U.S. patent application Ser. No. 12/892,424, any of which can be employed in any of the embodiments disclosed herein. Further, U.S. patent application Ser. No. 12/892,424 also discloses distributed digital data communications signals in a distributed antenna system which may also be distributed in the distributed antenna system 10 either in conjunction with the RF communications signals or not.

The distributed antenna system 10 has an antenna coverage area 20 that can be disposed about the remote unit 14. The antenna coverage area 20 of the remote unit 14 forms an RF coverage area 21. The central unit 12 is adapted to perform or to facilitate any one of a number of Radio-over-Fiber (RoF) applications, such as RF identification (RFID), wireless local-area network (WLAN) communication, or cellular phone service. Shown within the antenna coverage area 20 is a client device 24 in the form of a mobile device, which may be a cellular telephone as an example. The client device 24 can be any device that is capable of receiving RF communications signals. The client device 24 includes an antenna 26 (e.g., a wireless card) adapted to receive and/or send electromagnetic RF signals.

With continuing reference to FIG. 1, to communicate the electrical RF signals over the downlink optical fiber 16D to the remote unit 14, to in turn be communicated to the client device 24 in the antenna coverage area 20 formed by the remote unit 14, the central unit 12 includes a radio interface in the form of an electrical-to-optical (E/O) converter 28. The E/O converter 28 converts the downlink electrical RF signals 18D to downlink optical RF signals 22D to be communicated over the downlink optical fiber 16D. The remote unit 14 includes an optical-to-electrical (O/E) converter 30 to convert the received downlink optical RF signals 22D back to electrical RF signals to be communicated wirelessly through an antenna 32 of the remote unit 14 to the client device 24 located in the antenna coverage area 20.

Similarly, the antenna 32 is also configured to receive wireless RF communications from the client device 24 in the antenna coverage area 20. In this regard, the antenna 32 receives wireless RF communications from the client device 24 and communicates electrical RF signals representing the wireless RF communications to an E/O converter 34 in the remote unit 14. The E/O converter 34 converts the electrical RF signals into uplink optical RF signals 22U to be communicated over the uplink optical fiber 16U. An 0/E converter 36 provided in the central unit 12 converts the uplink optical RF signals 22U into uplink electrical RF signals, which can then be communicated as uplink electrical RF signals 18U back to a network or other source.

As noted, one or more of the network or other sources can be a cellular system, which may include a base station or base transceiver station (BTS). The BTS may be provided by a second party such as a cellular service provider, and can be co-located or located remotely from the central unit 12.

In a typical cellular system, for example, a plurality of BTSs is deployed at a plurality of remote locations to provide wireless telephone coverage. Each BTS serves a corresponding cell and when a mobile client device enters the cell, the BTS communicates with the mobile client device. Each BTS can include at least one radio transceiver for enabling communication with one or more subscriber units operating within the associated cell. As another example, wireless repeaters or bi-directional amplifiers could also be used to serve a corresponding cell in lieu of a BTS. Alternatively, radio input could be provided by a repeater, picocell, or femtocell, as other examples. In a particular exemplary embodiment, cellular signal distribution in the frequency range from 400 MHz to 2.7 GHz is supported by the distributed antenna system 10.

Although the distributed antenna system 10 in FIG. 1 allows for distribution of radio frequency (RF) communications signals; the distributed antenna system 10 is not limited to distribution of RF communications signals. Data communications signals, including digital data signals, for distributing data services could also be distributed in the distributed antenna system 10 in lieu of or in addition to RF communications signals. Also note that while the distributed antenna system 10 in FIG. 1 discussed below includes distribution of communications signals over optical fiber, the distributed antenna system 10 is not limited to distribution of communications signals over optical fiber. Distribution media could also include, but are not limited to, coaxial cable, twisted-pair conductors, wireless transmission and reception, and any combination thereof. Also, any combination can be employed that also involves optical fiber for portions of the distributed system.

A distributed antenna system, including the distributed antenna system 10 in FIG. 1, can be configured in MIMO configuration for MIMO operation. In this regard, FIG. 2 illustrates a schematic diagram of an exemplary MIMO optical fiber-based distributed antenna system 40 (hereinafter referred to as “MIMO distributed antenna system 40”). The MIMO distributed antenna system 40 is configured to operate in MIMO configuration. MIMO technology involves the use of multiple antennas at both a transmitter and receiver to improve communication performance. In this regard, a central unit 42 is provided that is configured to distribute downlink communications signals to one or more remote units 44. FIG. 2 only illustrates one remote unit 44, but note that a plurality of remote units 44 is typically provided. The remote units 44 are configured to wirelessly communicate the downlink communication signals to one or more client devices 46 that are in communication range of the remote unit 44. The remote units 44 may also be referred to as “remote antenna units 44” because of their wireless transmission over antenna functionality. The remote unit 44 is also configured to receive uplink communication signals from the client devices 46 to be distributed to the central unit 42. In this embodiment, an optical fiber communications medium 47 comprising at least one downlink optical fiber 48D and at least one uplink optical fiber 48U is provided to commutatively couple the central unit 42 to the remote units 44. The central unit 42 is also configured to receive uplink communication signals from the remote units 44 via the optical fiber communications medium 47, although more specifically over the at least one uplink optical fiber 48U. The client device 46 in communication with the remote unit 44 can provide uplink communication signals to the remote unit 44 which are then distributed over the optical fiber communications medium 47 to the remote unit 44 to be provided to a network or other source, such as a base station for example.

With continuing reference to FIG. 2, more detail will be discussed regarding the components of the central unit 42, the remote unit 44, and the client device 46 and the distribution of downlink communications signals. The central unit 42 is configured to receive electrical downlink MIMO communication signals 50D from outside the MIMO distributed antenna system 40 in a signal processor 52 and provide electrical uplink communications signals 50U received from client devices 46, to other systems. The signal processor 52 is configured to provide the electrical downlink communication signals 50D to a mixer 60, which may be an IQ signal mixer in this example. The mixer 60 in this embodiment is configured to convert the electrical downlink MIMO communication signals 50D to IQ signals. The mixer 60 is driven by a frequency signal 56 that is provided by a local oscillator 58. Frequency conversion is optional. In this embodiment, it is desired to up-convert the frequency of the electrical downlink MIMO communication signals 50D to a higher frequency to provide electrical downlink MIMO communication signals 66D to provide for a greater bandwidth capability before distributing the electrical downlink MIMO communications signals 66D to the remote units 44. For example, the up-conversion carrier frequency may be provided as an extremely high frequency (e.g. approximately 30 GHz to 300 GHz).

With continuing reference to FIG. 2, because the communication medium between the central unit 42 and the remote unit 44 is the optical fiber communications medium 47, the electrical downlink MIMO communication signals 66D are converted to optical signals by an electro-optical converter 67. The electro-optical converter 67 includes components to receive a light wave 68 from a light source 70, such as a laser. The light wave 68 is modulated by the frequency oscillations in the electrical downlink MIMO communication signals 66D to provide optical downlink MIMO communication signals 72D to be communicated over the downlink optical fiber 48D to the remote unit 44. The electro-optical converter 67 may be provided so that the electrical downlink MIMO communication signals 66D are provided as radio-over-fiber (RoF) communications signals over the downlink optical fiber 48D.

With continuing reference to FIG. 2, the optical downlink MIMO communication signals 72D are received by an optical bi-directional amplifier 74, which is then provided to a MIMO splitter 76 in the remote unit 44. The MIMO splitter 76 is provided so that the optical downlink MIMO communication signals 72D can be split among two separate communication paths 77(1), 77(2) to be radiated over two separate MIMO transmitter antennas 78(1), 78(2) provided in two separate MIMO transmitters 79(1), 79(2) configured in MIMO configuration. The MIMO splitter 76 in the remote unit 44 is an optical splitter since the received optical downlink MIMO communication signals 72D are optical signals. In each communication path 77(1), 77(2), optical-to-electrical converters 80(1), 80(2) are provided to convert the optical downlink MIMO communication signals 72D to electrical downlink MIMO communication signals 82D(1), 82D(2). In this embodiment, as will be discussed in more detail below, a delay element 84 is provided in one of the transmission paths 77(1), 77(2) to phase shift one of the optical downlink MIMO communication signals 72D(1), 72D(2) transmitted over one of the MIMO transmitter antennas 78(1), 78(2) to reduce or eliminate issues with a MIMO algorithm solving the channel matrix for received electrical downlink MIMO communication signals 82D by the client device 46.

With continuing reference to FIG. 2, the client device 46 includes two MIMO receivers 85(1), 85(2) that include MIMO receiver antennas 86(1), 86(2) also configured in MIMO configuration. The MIMO receiver antennas 86(1), 86(2) are configured to receive the electrical downlink MIMO communication signals 82D(1), 82D(2) wirelessly from the remote unit 44. Mixers 88(1), 88(2) are provided and coupled to the MIMO receiver antennas 86(1), 86(2) in the client device 46 to provide frequency conversion of the electrical downlink MIMO communication signals 82D(1), 82D(2). In this regard, a local oscillator 90 is provided that is configured to provide oscillation signals 92(1), 92(2) to the mixers 88(1), 88(2), respectively, for frequency conversion. In this embodiment, the electrical downlink MIMO communications signals 82D(1), 82D(2) are down converted back to their native frequency as received by the central unit 42. The down converted electrical downlink MIMO communication signals 82D(1), 82D(2) are then provided to a signal analyzer 92 in the client device 46 for any processing desired.

FIG. 3A illustrates a top view of a room 100 employing the exemplary MIMO distributed antenna system 40 in FIG. 2 to discuss performance of MIMO communications as affected by antenna placement. As illustrated in FIG. 3A, the two MIMO transmitter antennas 78(1), 78(2) of the remote unit 44 are shown as being located in the room 100. Similarly, a client device 46 is shown with its two MIMO receiver antennas 86(1), 86(2) configured to receive the electrical downlink MIMO communication signals 82D(1), 82D(2) from the two MIMO transmitter 81(1), 81(2) (FIG. 2) in MIMO configuration. The MIMO transmitter antennas 78(1), 78(2) in the MIMO transmitter 81(1), 81(2) in the remote unit 44 are separated by a distance D₁. The MIMO receiver antennas 86(1), 86(2) in the client device 46 are separated by a distance D₂. Issues can arise with MIMO algorithm being able to solve the channel matrix for received electrical downlink MIMO communication signals 82D(1), 82D(2) at the client device 46 as a function of the distance between the MIMO transmitter antennas 78(1), 78(2) in the remote unit 44, the distance between MIMO receiver antennas 86(1), 86(2) in the client device 46, and the distance D₃ between remote unit 44 and the client device 46. These issues are also referred to herein as interference issues.

A MIMO algorithm not being able to solve a channel matrix for the received electrical downlink MIMO communication signals 82D(1), 82D(2) can negatively affect communications performance. These issues with electrical downlink MIMO communication signals 82D(1), 82D(2) received by the MIMO receiver antennas 86(1), 86(2) can occur due to lack of spatial (i.e., phase) separation in the received electrical downlink MIMO communication signals 82D(1), 82D(2), especially in line-of-sight (LOS) communications. To illustrate the effect of these issues, FIG. 3B illustrates a graph 102 illustrating the exemplary measured performance degradation for a given placement distance between the MIMO transmitter antennas 78(1), 78(2) in FIG. 3A. The graph 102 in FIG. 3B illustrates the capacity on the y-axis in Gigabits per second (Gbs/s) versus the MIMO transmitter antennas 78(1), 78(2) separation distance D₁ in centimeters. As illustrated in the graph 102, at separation distances D₁ of approximately 42 centimeters (cm) and 85 cm, the communications capacity illustrated by a capacity curve 104 is severely degraded for the received electrical downlink MIMO communication signals 82D(1), 82D(2) by the MIMO receiver antennas 86(1), 86(2). Even at other distances, the capacity is severely degraded, as illustrated in the capacity curve 104. A degradation curve 106 in FIG. 3B illustrates the effect of a MIMO algorithm not being able to solve a channel matrix, which is complementary to the capacity curve 104.

FIG. 3C illustrates a graph 108 representing an exemplary effective communication coverage area provided by the distributed antenna system 40 in FIG. 2 according to the MIMO transmitter antennas 78(1), 78(2), separation distance D₁, the MIMO receiver antennas 86(1), 86(2), separation distance D₂ in FIG. 3A, and distance therebetween D₃. As illustrated in FIG. 3C, a desired antenna coverage area 109 is shown as being provided by the area formed inside a boundary line 110. However, an actual communication coverage area 113 for the remote unit 44 is provided inside the boundary line 112, illustrating the effect in reduction communication range of the remote unit 44.

To address these issues, FIGS. 4A-7C are provided to illustrate exemplary distributed antenna systems configured to reduce location-based interference in distributed antenna systems operating in multiple-input, multiple-output (MIMO) configuration. In these embodiments, to provide phase separation of MIMO communication signals received by MIMO receivers in client devices, multiple MIMO transmitters in a remote unit are each configured to employ multiple transmitter antennas. The multiple transmitter antennas are each configured to transmit communications signals in different polarization states. In certain embodiments, one of the MIMO communications signals is phase shifted in one of the polarization states to provide phase separation between MIMO communication signals received by the MIMO receivers.

In this regard, FIG. 4A illustrates an alternative MIMO distributed antenna system 40(1) similar to the MIMO distributed antenna system 40 in FIG. 2. The MIMO distributed antenna system 40(1) in FIG. 4A is configured to reduce or eliminate the inability of a MIMO algorithm not being able to solve a channel matrix of received downlink communication signals at a MIMO receiver in a client device based on the separation distance between MIMO transmitter antennas in a MIMO transmitter of a remote unit to reduce or eliminate performance degradation such as shown in FIGS. 3B and 3C above. The MIMO distributed antenna system 40(1) may include the same components in the MIMO distributed antenna system 40 in FIG. 2 unless otherwise noted in FIG. 4A.

With continuing reference to FIG. 4A, a central unit 42(1) is configured to receive the electrical downlink MIMO communications signals 50D as discussed in regard to FIG. 2. However, a signal processor 52(1) is configured to split the electrical downlink MIMO communications signals 50D into four (4) electrical downlink MIMO communications signals 50D(1)-50D(4) over four separate channels. A delay element 122 is provided in the central unit 42(1) to phase shift at least one of the electrical downlink MIMO communications signals 50D. Note that although the electrical downlink MIMO communications signal 50D(4) in this example, any other(s) downlink MIMO communications signal(s) 50D(1)-50D(3) could be phase shifted. The delay element 122 may be a tunable delay element that can be programmed or controlled to control the amount of phase shift, if desired. As will be discussed in more detail below, the phase shifting of one of the electrical downlink MIMO communications signals 50D will allow one of the polarization states provided by one of MIMO transmitters in a remote unit 44(1) to include phase separation between first through fourth electrical downlink MIMO communication signals 82D(1)-82D(4) that are received by the MIMO receivers to reduce or eliminate the inability of a MIMO algorithm to solve a channel matrix. Turning back to the central unit 42(1), electro-optical converters 67(1)-67(4) are provided to convert the electrical downlink MIMO communications signals 50D(1)-50D(4) into optical downlink MIMO communications signals 72D(1)-72D(4) provided over optical fiber communications medium 47(1).

With continuing reference to FIG. 4A, the remote unit 44(1) includes two MIMO transmitters 124(1), 124(2) in MIMO configuration. However, the MIMO transmitters 124(1), 124(2) each include two MIMO transmitter antennas 126(1)(1), 126(1)(2), and 126(2)(1), 126(2)(2). The first MIMO transmitter 124(1) includes the first MIMO transmitter antenna 126(1)(1) configured to radiate the first electrical downlink MIMO communications signals 82D(1) (after conversion from optical to electrical signals) in a first polarization 128(1), as indicated in FIG. 4A. The first MIMO transmitter 124(1) also includes the second MIMO transmitter antenna 126(1)(2) configured to radiate the second electrical downlink MIMO communications signal 82D(2) in a second polarization 128(2) different from the first polarization 128(1). In this manner, the first and second electrical downlink MIMO communications signals 82D(1), 82D(2) can be received by two different MIMO receiver antennas 130(1), 130(2) in MIMO receivers 132(1), 132(2), respectively, each configured to receive signals in different polarizations 128(1), 128(2) among the first and second polarizations 128(1), 128(2) without the MIMO algorithm being unable to solve the channel matrix. Thus, the MIMO receivers 132(1), 132(2) can receive the first and second electrical downlink MIMO communications signal 82D(1), 82D(2) in different polarizations 128(1), 128(2), respectively, from the first MIMO transmitter 124(1) so that a MIMO algorithm can solve the channel matrix for the first and second electrical downlink MIMO communications signal 82D(1), 82D(2). In this embodiment, the first polarization 128(1) is configured to be orthogonal to the second polarization 128(2) to maximize avoidance of the MIMO receivers 132(1), 132(2) receiving the incorrect electrical downlink MIMO communications signal 82D(1), 82D(2), but this configuration is not required.

With continuing reference to FIG. 4A, the second MIMO transmitter 124(2) in the remote unit 44(1) includes a third MIMO transmitter antenna 126(2)(1) configured to radiate the third electrical downlink MIMO communications signals 82D(3) (after conversion from optical to electrical signals) in the first polarization 128(1), as indicated in FIG. 4A. The second MIMO transmitter 124(2) also includes the fourth MIMO transmitter antenna 126(2)(2) configured to radiate the fourth electrical downlink MIMO communications signal 82D(4) in the second polarization 128(2) different from the first polarization 128(1). In this manner, the third and fourth electrical downlink MIMO communications signals 82D(3), 82D(4) can also be received by the two different MIMO receiver antennas 130(1), 130(2) in MIMO receivers 132(1), 132(2), respectively, each configured to receive signals in different polarizations 128(1), 128(2) among the first and second polarizations 128(1), 128(2). Thus, the MIMO receivers 132(1), 132(2) can receive the third and fourth electrical downlink MIMO communications signal 82D(3), 82D(4) in different polarizations, respectively, from the second MIMO transmitter 124(2) between the third and fourth electrical downlink MIMO communications signal 82D(3), 82D(4). The electrical downlink MIMO communications signals 82D(1)-82D(4) are received by the MIMO receivers 132(1), 132(2) and provided to a signal processor 134 and a MIMO processor 136 for processing.

As previously discussed above, the delay element 122 is provided in the central unit 42(1) to phase shift the electrical downlink MIMO communications signal 50D(4). This phase shift in turn causes the second and fourth electrical downlink MIMO communications signals 82D(2), 82D(4) to be received by the second MIMO receiver antennas 130(2) out of phase with the receipt of the first and third electrical downlink MIMO communications signals 82D(1), 82D(3) by the first MIMO receiver 132(1) which are in the first polarization 128(1). This reduces or eliminate the first and third electrical downlink MIMO communications signals 82D(1), 82D(3) being received by the first MIMO receiver 132(1) and the second and fourth electrical downlink MIMO communications signals 82D(2), 82D(4) being received by the second MIMO receiver 132(2).

The phase shift can be provided in other areas of a MIMO distributed antenna system other than in the central unit, as provided in the MIMO distributed antenna system 40(1) in FIG. 4A. In this regard, FIG. 4B is a schematic diagram of another MIMO optical fiber-based distributed antenna system 40(2) (“MIMO distributed antenna system 40(2)”) employing a delay element 140 in the form of an optical phase shifter in the optical fiber communications medium 47(1). The delay element 140 can be tunable to allow for the phase shift to be controlled and tuned. The delay element 140 may be an additional length of optical fiber to make the corresponding downlink optical fibers in the optical fiber communications medium 47(1) carrying the optical downlink MIMO communications signal 72D(1) longer than the other downlink optical fibers of the optical fiber communications medium 47(1). Common elements between the MIMO distributed antenna system 40(1) in FIG. 4A and the MIMO distributed antenna system 40(2) in FIG. 4B are noted with common element numbers and will not be re-described. In this embodiment, the delay element 140 is configured to optically phase shift the optical downlink MIMO communications signal 72D(4) received by the second MIMO transmitter 124(2) and transmitted by the second MIMO transmitter 124(2) to the client device 46(1). The central unit 42(2) in FIG. 4B does not include a delay element to phase shift downlink electrical communications signals like provided in the central unit 42(1) in FIG. 4A.

As previously discussed above with regard to FIGS. 4A and 4B, a delay element can be provided in the central unit 42(1), 42(2) and/or the optical fiber communications medium 47(1) to phase shift the electrical downlink MIMO communications signal 50D(4). In this regard, FIG. 4C is a schematic diagram of another MIMO optical fiber-based distributed antenna system 40(3) (“MIMO distributed antenna system 40(3)”) employing a delay element 142 in the form of an electrical phase shifter in the remote unit 44(2). Common elements between the MIMO distributed antenna system 40(3) in FIG. 4C and the MIMO distributed antenna systems 40(1), 40(2) in FIGS. 4A and 4B are noted with common element numbers and will not be re-described. In this embodiment, a signal processor 144 in the remote unit 44(2) receives the optical downlink MIMO communications signals 72D(1)-72D(4) and converts these signals into electrical downlink MIMO communications signals 82D(1)-82D(4) in an optical-to-electrical converter. The delay element 142 is configured to electrically phase shift the electrical downlink MIMO communications signal 82D(4) received and transmitted by the second MIMO transmitter 124(2) in the remote unit 44(2) to the client device 46(1) so that a MIMO algorithm can solve the channel matrix for the electrical downlink MIMO communications signal 82D(1)-82D(4).

To illustrate the performance in the MIMO distributed antenna systems 40(1)-40(3) in FIGS. 4A-4C, FIG. 5A illustrates a graph 150 illustrating the exemplary measured performance degradation for a given placement distance between the MIMO transmitters 124(1), 124(2). The graph 102 in FIG. 3B illustrates the capacity on the y-axis in Gigabits per second (Gbs/s) versus the MIMO transmitter antennas 78(1), 78(2) separation distance in centimeters. As illustrated in the graph 150, for a given separation distance the communications capacity illustrated by a capacity curve 152 is not substantially degraded for received electrical downlink MIMO communication signals 82D(1), 82D(2) by the MIMO receiver antennas 86(1), 86(2). The degradation curve 154 in FIG. 5A illustrates the effect of a MIMO algorithm having issues solving a channel matrix that may be present when techniques described above for MIMO distributed antenna systems 40(1)-40(3) are not employed. FIG. 5B illustrates a graph 160 representing an exemplary effective communication coverage area provided by the MIMO distributed antenna systems 40(1)-40(3) in FIGS. 4A-4C according to the MIMO transmitter 124(1), 124(2) separated by a given distance. As illustrated in FIG. 5B, a desired antenna coverage area 162 is shown as being provided by the area formed inside the boundary line 164.

FIG. 5C is a graph 170 illustrating an exemplary effective antenna coverage versus placement distance between MIMO transmitters 124(1), 124(2) in the distributed antenna systems 40(1)-40(3) in FIGS. 4A-4C, for a two (2) cm placement distance between the MIMO receivers 132(1), 132(2). FIG. 5D is a graph 180 illustrating an exemplary effective antenna coverage versus placement distance between MIMO transmitters 124(1), 124(2) in the distributed antenna systems 40(1)-40(3) in FIGS. 4A-4C, for a 10 cm placement distance between the MIMO receives 132(1), 132(2). Coverage curves 172, 182 illustrate the capacity when the techniques described above for the MIMO distributed antenna systems 40(1)-40(3) are employed. Coverage curves 174, 184 illustrate the capacity that may be present when the techniques described above for the MIMO distributed antenna systems 40(1)-40(3) are not employed.

Other configurations and techniques may also be possible to provide phase separation of MIMO communication signals received by MIMO receivers in client devices, multiple MIMO transmitters in a remote unit are each configured to employ multiple transmitter antennas. In this regard, FIG. 6 is a schematic diagram of another exemplary remote unit 44(3) that provides phase separation of the downlink electrical MIMO communication signals 82D(1)-82D(4) received by the MIMO receivers 132(1), 132(2). The remote unit 44(3) may be employed in a MIMO distributed antenna system, including the MIMO distributed antenna systems 40(1)-140(3) described in FIGS. 4A-4C above. Common elements between the components in FIG. 6 and the MIMO distributed antenna systems 40(1)-40(3) in FIGS. 4A-4C are noted with common element numbers and will not be re-described. In this embodiment, instead of providing a delay element to provide phase shift, the MIMO transmitter antennas 126(1)(1), 126(1)(2) in the MIMO transmitter 124(1), 124(2) are offset in distance at distance D₄. A small offset distance may be sufficient to significantly improve capacity. This separation distance provides a phase shift in the electrical downlink MIMO communications signal 82D(1).

FIG. 7A is a graph 190 illustrating an exemplary effective antenna coverage versus placement distance between MIMO transmitters 124(1), 124(2) in a MIMO distributed antenna system 40(1)-40(3) employing the remote unit 44(3) in FIG. 6, for a two (2) cm placement distance between the MIMO receivers 132(1), 132(2). FIG. 7B is a graph 200 illustrating an exemplary effective antenna coverage versus placement distance between MIMO transmitters 124(1), 124(2) in a MIMO distributed antenna system 40(1)-40(3) employing the remote unit 44(3) in FIG. 6, for a ten (10) cm placement distance between the MIMO receivers 132(1), 132(2). Coverage curves 192, 202 illustrate the capacity when the remote unit 44(3) is employed. Coverage curves 194, 204 illustrate the capacity that may be present when the techniques described above for the MIMO distributed antenna systems 40(1)-40(3) and the remote unit 44(3) are not employed. FIG. 7C is a graph 210 illustrating an exemplary effective antenna coverage for a given offset distance between MIMO transmitter antennas 126(1)(1), 126(1)(2) in the first MIMO transmitter 124(1) of the remote unit 44(3) in FIG. 6.

It may also be desired to provide high-speed wireless digital data service connectivity with remote units in the MIMO distributed antenna systems disclosed herein. One example would be WiFi. WiFi was initially limited in data rate transfer to 12.24 Mb/s and is now provided at data transfer rates of up to 54 Mb/s using WLAN frequencies of 2.4 GHz and 5.8 GHz. While interesting for many applications, WiFi has proven to have too small a bandwidth to support real time downloading of uncompressed high definition (HD) television signals to wireless client devices. To increase data transfer rates, the frequency of wireless signals could be increased to provide larger channel bandwidth. For example, an extremely high frequency in the range of 30 GHz to 300 GHz could be employed. For example, the sixty (60) GHz spectrum is an EHF that is an unlicensed spectrum by the Federal Communications Commission (FCC) and that could be employed to provide for larger channel bandwidths. However, high frequency wireless signals are more easily attenuated or blocked from traveling through walls or other building structures where distributed antenna systems are installed.

Thus, the embodiments disclosed herein can include distribution of extremely high frequency (EHF) (i.e., approximately 30—approximately 300 GHz), as a non-limiting example. The MIMO distributed antenna systems disclosed herein can also support provision of digital data services to wireless clients. The use of the EHF band allows for the use of channels having a higher bandwidth, which in turn allows more data intensive signals, such as uncompressed HD video to be communicated without substantial degradation to the quality of the video. As a non-limiting example, the distributed antenna systems disclosed herein may operate at approximately sixty (60) GHz with approximately seven (7) GHz bandwidth channels to provide greater bandwidth to digital data services. The distributed antenna systems disclosed herein may be well suited to be deployed in an indoor building or other facility for delivering of digital data services.

It may be desirable to provide MIMO distributed antenna systems, according to the embodiments disclosed herein, that provide digital data services for client devices. For example, it may be desirable to provide digital data services to client devices located within a distributed antenna system. Wired and wireless devices may be located in the building infrastructures that are configured to access digital data services. Examples of digital data services include, but are not limited to, Ethernet, WLAN, WiMax, WiFi, DSL, and LTE, etc. Ethernet standards could be supported, including but not limited to, 100 Mb/s (i.e., fast Ethernet) or Gigabit (Gb) Ethernet, or ten Gigabit (10 G) Ethernet. Examples of digital data services include, but are not limited to, wired and wireless servers, wireless access points (WAPs), gateways, desktop computers, hubs, switches, remote radio heads (RRHs), baseband units (BBUs), and femtocells. A separate digital data services network can be provided to provide digital data services to digital data devices.

FIG. 8 is a schematic diagram representation of additional detail illustrating components that could be employed in any of the components or devices disclosed herein, but only if adapted to execute instructions from an exemplary computer-readable medium to perform any of the functions or processing described herein. In this regard, such component or device may include a computer system 220 within which a set of instructions for performing any one or more of the location services discussed herein may be executed. The computer system 220 may be connected (e.g., networked) to other machines in a LAN, an intranet, an extranet, or the Internet. While only a single device is illustrated, the term “device” shall also be taken to include any collection of devices that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. The computer system 220 may be a circuit or circuits included in an electronic board card, such as, a printed circuit board (PCB), a server, a personal computer, a desktop computer, a laptop computer, a personal digital assistant (PDA), a computing pad, a mobile device, or any other device, and may represent, for example, a server or a user's computer.

The exemplary computer system 220 in this embodiment includes a processing device or processor 222, a main memory 224 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM), such as synchronous DRAM (SDRAM), etc.), and a static memory 226 (e.g., flash memory, static random access memory (SRAM), etc.), which may communicate with each other via a data bus 228. Alternatively, the processing device 222 may be connected to the main memory 224 and/or static memory 226 directly or via some other connectivity means. The processing device 222 may be a controller, and the main memory 224 or static memory 226 may be any type of memory.

The processing device 222 represents one or more general-purpose processing devices, such as a microprocessor, central processing unit, or the like. More particularly, the processing device 222 may be a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, a processor implementing other instruction sets, or other processors implementing a combination of instruction sets. The processing device 222 is configured to execute processing logic in instructions 230 for performing the operations and steps discussed herein.

The computer system 220 may further include a network interface device 232. The computer system 220 also may or may not include an input 234, configured to receive input and selections to be communicated to the computer system 220 when executing instructions. The computer system 220 also may or may not include an output 236, including but not limited to a display, a video display unit (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device (e.g., a keyboard), and/or a cursor control device (e.g., a mouse).

The computer system 220 may or may not include a data storage device that includes instructions 238 stored in a computer-readable medium 240. The instructions 238 may also reside, completely or at least partially, within the main memory 224 and/or within the processing device 222 during execution thereof by the computer system 220, the main memory 224 and the processing device 222 also constituting computer-readable medium. The instructions 238 may further be transmitted or received over a network 242 via the network interface device 232.

While the computer-readable medium 240 is shown in an exemplary embodiment to be a single medium, the term “computer-readable medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “computer-readable medium” shall also be taken to include any medium that is capable of storing, encoding, or carrying a set of instructions for execution by the processing device and that cause the processing device to perform any one or more of the methodologies of the embodiments disclosed herein.

The embodiments disclosed herein include various steps. The steps of the embodiments disclosed herein may be formed by hardware components, software components, and combinations thereof.

The embodiments disclosed herein may be provided as a computer program product, or software, that may include a machine-readable medium (or computer-readable medium) having stored thereon instructions, which may be used to program a computer system (or other electronic devices) to perform a process according to the embodiments disclosed herein.

Unless specifically stated otherwise and as apparent from the previous discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing,” “computing,” “determining,” “displaying,” or the like, refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data and memories represented as physical (electronic) quantities within the computer system's registers into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission, or display devices.

The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. In addition, the embodiments described herein are not described with reference to any particular programming language.

Those of skill in the art will further appreciate that the various illustrative logical blocks, modules, circuits, and algorithms described in connection with the embodiments disclosed herein may be implemented as electronic hardware, instructions stored in memory or in another computer-readable medium and executed by a processor or other processing device, or combinations of both. The components of the distributed antenna systems described herein may be employed in any circuit, hardware component, integrated circuit (IC), or IC chip, as examples. Memory disclosed herein may be any type and size of memory and may be configured to store any type of information desired. To clearly illustrate this interchangeability, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. How such functionality is implemented depends on the particular application, design choices, and/or design constraints imposed on the overall system.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. Furthermore, a controller may be a processor.

The embodiments disclosed herein may be embodied in hardware and in instructions that are stored in hardware, and may reside, for example, in RAM, flash memory, ROM, Electrically Programmable ROM (EPROM), Electrically Erasable Programmable ROM (EEPROM), registers, a hard disk, a removable disk, a CD-ROM, or any other form of computer-readable medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor.

It is also noted that the operational steps described in any of the exemplary embodiments herein are described to provide examples and discussion. The operations described may be performed in numerous different sequences other than the illustrated sequences. Furthermore, operations described in a single operational step may actually be performed in a number of different steps.

Further and as used herein, it is intended that terms “fiber optic cables” and/or “optical fibers” include all types of single mode and multi-mode light waveguides, including one or more optical fibers that may be upcoated, colored, buffered, ribbonized, and/or have other organizing or protective structure in a cable such as one or more tubes, strength members, jackets, or the like.

It is to be understood that the description and claims are not to be limited to the specific embodiments disclosed, and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. 

What is claimed is:
 1. A multiple-input multiple-output (MIMO) remote unit configured to wirelessly distribute MIMO communications signals to wireless client devices, comprising: a first MIMO transmitter comprising a first MIMO transmitter antenna configured to transmit MIMO communications signals in a first polarization and a second MIMO transmitter antenna configured to transmit MIMO communications signals in a second polarization different from the first polarization; and a second MIMO transmitter comprising a third MIMO transmitter antenna configured to transmit MIMO communications signals in the first polarization and a fourth MIMO transmitter antenna configured to transmit MIMO communications signals in the second polarization; the first MIMO transmitter configured to: receive a first optical downlink MIMO communications signal in a first phase over a first downlink communications medium, and transmit the first optical downlink MIMO communications signal wirelessly as a first downlink MIMO communications signal over the first MIMO transmitter antenna in the first polarization; and receive a second optical downlink MIMO communications signal in the first phase over a second downlink communications medium, and transmit the second optical downlink MIMO communications signal wirelessly as a second downlink MIMO communications signal over the second MIMO transmitter antenna in the second polarization; the second MIMO transmitter configured to: receive a third optical downlink MIMO communications signal in the first phase over a third downlink communications medium, and transmit the third optical downlink MIMO communications signal wirelessly as a third downlink MIMO communications signal over the third MIMO transmitter antenna in the first polarization; and receive a fourth optical downlink MIMO communications signal over a fourth downlink communications medium, and transmit the fourth optical downlink communications signal in a second phase shifted from the first phase, wirelessly as a fourth downlink MIMO communications signal over the fourth MIMO transmitter antenna in the second polarization.
 2. The MIMO remote unit of claim 1, wherein: the first MIMO transmitter further comprises a first optical-to-electrical (0/E) converter configured to convert the first optical downlink MIMO communications signal to the first downlink MIMO communications signal and a second 0/E converter configured to convert the second optical downlink MIMO communications signal to the second MIMO downlink communications signal; and the second MIMO transmitter further comprises a third 0/E converter configured to convert the third optical downlink MIMO communications signal to the third downlink MIMO communications signal and a fourth 0/E converter configured to convert the fourth optical downlink MIMO communications signal to the second downlink MIMO communications signal.
 3. The MIMO remote unit of claim 2, wherein: the first MIMO transmitter is further configured to transmit the first and second downlink MIMO communications signals wirelessly to a line-of-sight (LOS) wireless client; and the second MIMO transmitter is configured to transmit the third and fourth downlink MIMO communications signals wirelessly to the line-of-sight (LOS) wireless client.
 4. The MIMO remote unit of claim 2, further comprising at least one phase shifter configured to phase shift the fourth optical downlink MIMO communications signal to the second phase.
 5. The MIMO remote unit of claim 2, wherein the second MIMO transmitter is configured to receive the fourth optical downlink MIMO communications signal in the second phase as a result of a phase shift of the fourth optical downlink MIMO communications signal in a central unit.
 6. The MIMO remote unit of claim 2, wherein the second MIMO transmitter is configured to receive the fourth optical downlink MIMO communications signal in the second phase as a result of a phase shift of the fourth optical downlink MIMO communications signal in the fourth downlink communications medium.
 7. The MIMO remote unit of claim 6, wherein the fourth downlink communications medium is positioned between a central unit of a wireless communications system and the second MIMO transmitter.
 8. The MIMO remote unit of claim 2, wherein the third MIMO transmitter antenna is phase offset from the fourth MIMO transmitter antenna by the third MIMO transmitter antenna being positioned in distance from the fourth MIMO transmitter antenna.
 9. The MIMO remote unit of claim 2, wherein the first MIMO transmitter antenna is position offset from the second MIMO transmitter antenna by positioning the first MIMO transmitter antenna in distance from the second MIMO transmitter antenna.
 10. A method of transmitting multiple-input multiple-output (MIMO) communications signals to wireless client devices, comprising: receiving a first optical downlink MIMO communications signal in a first phase over a first downlink communications medium; transmitting the first optical downlink MIMO communications signal wirelessly as a first downlink MIMO communications signal over a first MIMO transmitter antenna in a first polarization; and receiving a second optical downlink MIMO communications signal in the first phase over a second downlink communications medium; transmitting the second optical downlink MIMO communications signal wirelessly as a second downlink MIMO communications signal over a second MIMO transmitter antenna in a second polarization; receiving a third optical downlink MIMO communications signal in the first phase over a third downlink communications medium; transmitting the third optical downlink MIMO communications signal wirelessly as a third downlink MIMO communications signal over a third MIMO transmitter antenna in the first polarization; receiving a fourth optical downlink MIMO communications signal over a fourth downlink communications medium; and transmitting the fourth optical downlink MIMO communications signal in a second phase shifted from the first phase, wirelessly as a fourth downlink MIMO communications signal over a fourth MIMO transmitter antenna in the second polarization.
 11. The method of claim 10, further comprising transmitting the first downlink MIMO communications signal wirelessly to a line-of-sight (LOS) wireless client.
 12. The method of claim 11, further comprising phase shifting the fourth optical downlink MIMO communications signal to the second phase.
 13. The method of claim 11, further comprising receiving the fourth optical downlink MIMO communications signal in the second phase from a central unit that phase shifts the fourth optical downlink MIMO communications signal from the first phase to the second phase.
 14. The method of claim 11, further comprising receiving the fourth optical downlink MIMO communications signal in the second phase via the fourth downlink communications medium configured to phase shift the fourth optical downlink MIMO communications signal from the first phase to the second phase.
 15. The method of claim 10, further comprising phase offsetting the third MIMO transmitter antenna from the fourth MIMO transmitter antenna by positioning the third MIMO transmitter antenna in distance from the fourth MIMO transmitter to phase shift the fourth optical downlink MIMO communications signal to the second phase.
 16. The method of claim 10, further comprising position offsetting the first MIMO transmitter antenna from the second MIMO transmitter antenna by positioning the first MIMO transmitter antenna in distance from the second MIMO transmitter antenna.
 17. A distributed antenna system for distributing multiple-input multiple-output (MIMO) communications signals to wireless client devices, comprising: a central unit comprising a central unit transmitter configured to transmit a first optical downlink MIMO communications signal over a first downlink communications medium, a second optical downlink MIMO communications signal over a second downlink communications medium, a third optical downlink MIMO communications signal over a third downlink communications medium, and a fourth optical downlink MIMO communications signal over a fourth downlink communications medium; and a plurality of remote units in communications with the central unit, a first of the remote units comprising: a first MIMO transmitter comprising a first MIMO transmitter antenna configured to transmit MIMO communications signals in a first polarization and a second MIMO transmitter antenna configured to transmit MIMO communications signals in a second polarization different from the first polarization; a second MIMO transmitter comprising a third MIMO transmitter antenna configured to transmit MIMO communications signals in the first polarization and a fourth MIMO transmitter antenna configured to transmit MIMO communications signals in the second polarization; the first MIMO transmitter configured to: receive the first optical downlink MIMO communications signal in a first phase over the first downlink communications medium, and transmit the first optical downlink MIMO communications signal wirelessly as a first downlink MIMO communications signal over the first MIMO transmitter antenna in the first polarization; and receive the second optical downlink MIMO communications signal in the first phase over the second downlink communications medium, and transmit the second optical downlink MIMO communications signal wirelessly as a second downlink MIMO communications signal over the second MIMO transmitter antenna in the second polarization; the second MIMO transmitter configured to: receive the third optical downlink MIMO communications signal in the first phase over the third downlink communications medium, and transmit the third optical downlink MIMO communications signal wirelessly as a third downlink MIMO communications signal over the third MIMO transmitter antenna in the first polarization; and receive the fourth optical downlink MIMO communications signal over the fourth downlink communications medium, and transmit the fourth downlink MIMO communications signal in a second phase shifted from the first phase, wirelessly as a fourth downlink MIMO communications signal over the fourth MIMO transmitter antenna in the second polarization; and at least one phase shifter configured to phase shift the fourth optical downlink MIMO communications signal to the second phase.
 18. The distributed antenna system of claim 17, wherein: the first MIMO transmitter is further configured to transmit the first and second downlink MIMO communications signals wirelessly to a line-of-sight (LOS) wireless client; and the second MIMO transmitter is configured to transmit the third and fourth downlink MIMO communications signals wirelessly to the LOS wireless client.
 19. The distributed antenna system of claim 17, wherein the first downlink communications medium comprises at least one optical fiber. 